Search

Your search keyword '"Prager, Jens"' showing total 31 results
Start Over Author "Prager, Jens" Publication Year Range Last 10 years
31 results on '"Prager, Jens"'

1. Experimental validation of an inverse method for defect reconstruction in a 2D waveguide model

Author

Bulling, Jannis, Jurgelucks, Benjamin, Prager, Jens, and Walther, Andrea

Subjects
Mathematics - Numerical Analysis, 65K99, G.1.6
Abstract

Defect reconstruction is essential in non-destructive testing and structural health monitoring with guided ultrasonic waves. This paper presents an algorithm for reconstructing notches in steel plates which can be seen as artificial defects representing cracks by comparing measured results with those from a simulation model. The model contains a parameterized notch, and its geometrical parameters are to be reconstructed. While the algorithm is formulated and presented in a generalized form for many different defect types, a special case of guided wave propagation is used to investigate one of the simplest possible simulation models that discretizes only the cross-section of the steel plate. An efficient simulation model of the plate cross-section is obtained by the semi-analytical Scaled Boundary Finite Element Method. The reconstruction algorithm applied is gradient-based, and Algorithmic Differentiation calculates the gradient. The dedicated experimental setup excites nearly plane wave fronts propagating orthogonal to the notch. A scanning Laser Doppler Vibrometer records the velocity field at certain points on the plate surface as input to the reconstruction algorithm. Using two plates with notches of different depths, it is demonstrated that accurate geometry reconstruction is possible., Comment: 13 pages, 11 figures

Published
2023

4. Defect reconstruction in a 2D semi-analytical waveguide model via derivative-based optimization

Author

Bulling, Jannis, Jurgelucks, Benjamin, Prager, Jens, and Walther, Andrea

Subjects
Mathematics - Numerical Analysis, 65M32
Abstract

This paper considers the reconstruction of a defect in a two-dimensional waveguide during non-destructive ultrasonic inspection using a derivative-based optimization approach. The propagation of the mechanical waves is simulated by the Scaled Boundary Finite Element Method (SBFEM) that builds on a semi-analytical approach. The simulated data is then fitted to a given set of data describing the reflection of a defect to be reconstructed. For this purpose, we apply an iteratively regularized Gauss-Newton method in combination with algorithmic differentiation to provide the required derivative information accurately and efficiently. We present numerical results for three different kinds of defects, namely a crack, a delamination, and a corrosion. These examples show that the parameterization of the defect can be reconstructed efficiently and robustly in the presence of noise., Comment: 22 pages, 11 figures

Published
2021
Full Text
View/download PDF

5. Sensitivity of Ultrasonic Guided Waves to Elastic Constants: A Numerical Study

Author

Bulling, Jannis, Franosch, Georg, Lugovtsova, Yevgeniya, Prager, Jens, di Prisco, Marco, Series Editor, Chen, Sheng-Hong, Series Editor, Vayas, Ioannis, Series Editor, Kumar Shukla, Sanjay, Series Editor, Sharma, Anuj, Series Editor, Kumar, Nagesh, Series Editor, Wang, Chien Ming, Series Editor, Rizzo, Piervincenzo, editor, and Milazzo, Alberto, editor

Published
2021
Full Text
View/download PDF

13. Deutsche Normungsroadmap Künstliche Intelligenz Ausgabe 2

Author

Adler, Rasmus, Alcala, Araceli, Anton, Marie, Armbruster, Tristan, Arntzen, Stefan, Aschenbrenner, Doris, Klaus-Dieter Axt, Baumgartner, Renate, Becker, Nikolas, Beiter, Rebecca, Bendig, Thomas, Benecke, Ralf, Benner, Philipp, Bernhardt, Bastian, Beyer, Paul, Bich, Karsten, Biehler, Jan, Bieringer, Lukas, Binder, Andreas, Birska, Sylwia, Blum, André, Böhm, John, Bohn, Jürgen, Bollgrün, Patrick, Börkircher, Mikko, Borowski, Kevin, Bracht, Oliver, Brand, Matthias, Buchsbaum, Katharina, Budde, Lena Marie, Bühler, Joachim, Bunte, Andreas, Burchardt, Aljoscha, Burton, Simon, Büttel, Tim, Coester, Ulla, Cremers, Armin B., Czarny, Damian A., Da Silva, Lucas, Dang, David, Däßler, Klaus, De Meer, Jan, Demel, Axel, Deussen, Peter, Dickhaut, Ernestine, Dittrich, Eckhard, Dittrich, Alexander, Khac, Lilian Do, Dotzauer, Felix, Drzyzga, Gilbert, Ebers, Martin, Elmas, Filiz, Elmer, Stefan, Esche, Marko, Fehlandt, Benjamin, Féret, Leander, Fetic, Lajla, Fliehe, Marc, Fligge-Niebling, Julia, Flögel, Werner, Frank, Matthias, Franken, Annika, Fränzle, Martin, Fraunholz, Christian, Frierson, Charlotte, Gauer, Florian, Gause, Clemens, Gautier, Antoine, Gebauer, Marc, Geiger, Bernd, Genovesi, Sergio, Gerst, Detlef, Geschwill, Simon, Gesmann-Nuissl, Dagmar, Glasmeier, Nora Helena, Glatzner, Ludwig, Gnaudschun, Jens, Goebel, Marius, Grau, Dominik, Gromov, Viacheslav, Großmann, Jürgen, Grotepass, Jürgen, Gruchmann, Yvonne, Günther, Norman, Haimerl, Martin, Hattenkofer, Christian, Hauer, Marc, Haufe, Stefan, Heider, Elias, Heiles, Jürgen, Heinemann, Tobias, Hein, Tabea, Heinemann, Claudia, Henseler, Christoph, Hildesheim, Wolfgang, Hilgert, Barbara, Höhndorf, Lukas, Holoyad, Taras, Hösl, Maximilian, Jaschke, Alexander, Jung, Barbara, Just, Vanessa, Kacyniak, Agnieszka, Kaiser, Thomas, Kärkkäinen, Leo, Kiefer, Jan, Kim, So-Jin, Kirsch, Roland, Nils-Olaf Klabunde, Kläs, Michael, Kleen, Philip, Kleinfeld, Anette, Klingel, Anita, Klippert, Jürgen, Kloiber, Julia, Knaak, Mirko, Knauer, David, Knauer, Ricardo, Knaut, Andrea, Knecht, Franz, Knicker, Mario, Knödler, Marco, Knopf, Harry, Köhler, Martin F., Kolf, Christian, Kolliarakis, Georgios, Koska, Christopher, Kosslers, Sebastian, Kossow, Roland, Kothe, Stefan, Kotte, Sebastian, Krafft, Tobias D., Kratzer, Klaus, Kraus, Tom, Krebsz, Markus, Kremer, Tim, Kriegsmann, Sebastian, Kröll, Mirco, Krüger, Antonio, Krüger, Katja, Brandao, Jacques Kruse, Kubes, Tanja, Kuch, Susanne, Kunkel, Stefan, Küttner, Benjamin, Lachenmaier, Jens F., Laible, Holger, Lakermann, Joel, Lang, Fredi, Latniak, Erich, Lederer, Elisa, Legat, Christoph, Lehmhaus, Lorenz, Mahei Manhai Li, Lipka, Michael, Loevenich, Daniel, Lorenz, Jeanette Miriam, Löwen, Ulrich, Ma, Jackie, Maack, Stefan, Mackert, Manuela, Mahr, Sabine, Margreiter, Maximilian, Markert, Karla, Maspfuhl, Oliver, Matthias, Isabel, Matzke, Gerd, Meeß, Henri, Merget, Iris, Meschede, Ralf, Meyer, Martin, Meyer, Olga, Meyne, Sascha, Mihatsch, Alexander, Mirnig, Alexander G., Mockenhaupt, Andreas, Möhlmann, Eike, Mörike, Michael, Müller, Andreas W., Müller, Christian, Nad, Tomislav, Nahler, Gert, Nawroth, Andreas, Neuhüttler, Jens, Neumann-Brosig, Matthias, Neveling, Marc, Nickel, Peter, Niehaus, Jürgen, Nienaber, Reimund, Nöbel, Johannes, Nowack, Antje, O'Sullivan, Shane, Obert, Otto, Ohliger, Ursula, Page, Rebecca, Papenbrock, Jochen, Pechmann, Ludwig, Peifer, Yannick, Pekerman, Robin H., Pentenrieder, Annelie, Peters, Christoph, Petsch, Fabian, Petschick, Katharina, Peylo, Christoph, Pflumm, Daniel, Philipp, Patrick, Pöhls, Heinrich C., Poignée, Frank, Poretschkin, Maximilian, Portier, Martin, Prager, Jens, Putzer, Henrik J., Rabe, Alexander, Rauh, Peter, Reese, Hendrik A., Rehm, Georg, Reinel, Claudia, Rennoch, Alex, Roleff, Klaus, Roscher, Karsten, Rosenthal, Michael, Rösler, Jan, Röttger, Nils, Runze, Gerhard, Ruskowski, Martin, Saerbeck, Martin, Sanner, Peter K., Sawilla, Ingo, Schacht, Mario, Schemel, Peter, Scheurenbrand, Kim Marvin, Schildt, Maximilian, Schirgi, David, Schleipen, Miriam, Schlesinger, Dirk, Schlicker, Nadine, Schmid, Thomas, Michael-Christian Schmidt, Schmidt, Thomas, Schmidt, Christoph, Schmidtke, Jörg, Schmiedchen, Frank, Schmitz, Thorsten, Schneider, Jonas, Schoepe, Detlef, Schröder, Wolfgang M., Schröter, Welf, Schlug, Stephan, Schüßler, Tim, Schütte, Jan Fiete, Schwendicke, Falk, Seeliger, Adrian, Seifert, Eberhard K., Seitz, Jan, Annegrit Seyerlein-Klug, Shahinfar, Fatemeh, Simbeck, Katharina, Skuin, Andreas, Sliwa, Ariana, Spallek, Reiner, Spangenberg, Felix, Sperl, Philip, Spitzer, Patrick, Spreiter, Lucas, Steimers, André, Steininger, Rosmarie, Steinke, Jannis, Stemmer, Mira, Stock, Patricia, Stoll, Julia, Strobel, Christina, Stuch, Oliver, Stürenburg, Johannes, Surdina, Alexandra, Ernö Szivek, Tagiew, Rustam, Ternes, Neal, Terstegen, Sebastian, Tettke, Martin, Traphöner, Ralph, Traschewski, Holk, Treier, Volker, Trippel, Thorsten, Unverricht, Kristina, Usländer, Thomas, Uslar, Mathias, Van Hasselt, Tobias, Veith, Eric MSP, Vijayagopal, Sharan, Vock, Silvia, Vollmer, Thomas, Von Geibler, Justus, Von Twickel, Arndt, Waechter, Sabine, Wagner, Kirsten, Wagner-Stürz, David, Wahl, Siegfried, Wahlster, Wolfgang, Walter, Robert, Waschulzik, Thomas, Waurick, Steffen, Wedel, Marco, Wegener, Dieter, Weicken, Eva, Wenzel, Felix, Westhoven, Martin, Wildpanner, Bernd, Winter, Dorothea, Winter, Johannes, Winter, Mario, Winterhalter, Christoph, Wirjadi, Oliver, Wohlrapp, Sebastian, Wolf, Susanna, Wrobel, Stefan, Wunderle, Alexander, Wutz, Michael, YiJunsong, Jason, Zaunseder, Sebastian, Zehlike, Meike, Zidowitz, Stephan, Ziegler, Wolfgang, Ziehn, Jens, Zillner, Sonja, and Zucker, Bettina

Published
2022
Full Text
View/download PDF

17. Large eddy simulation of the dynamics of lean premixed flames using global reaction mechanisms calibrated for CH4–H2 fuel blends.

Author

Garcia, Alex M., Le Bras, Sophie, Prager, Jens, Häringer, Matthias, and Polifke, Wolfgang

Subjects
LARGE eddy simulation models, COUNTERFLOWS (Fluid dynamics), HYDROGEN flames, FLAME, HEAT transfer, IMPULSE response, BLAST effect, SPEED
Abstract

The effects of hydrogen addition on the flame dynamics of a bluff-body stabilized methane–hydrogen turbulent flame are studied with large eddy simulation (LES). The LES is carried out with the thickened flame model and global kinetic mechanisms calibrated for the methane–hydrogen mixtures. Conjugate heat transfer is included in the LES to consider a proper wall temperature while the flame shape changes with hydrogen addition. A data-based calibration of the global mechanisms is done with a methodology based on reproducing the net species production rates computed with a detailed kinetic mechanism. An improvement in this methodology is proposed to increase its accuracy and reliability. The calibrated mechanisms accurately describe the variation of the laminar flame speed and the thermal flame thickness with hydrogen addition and equivalence ratio in a freely propagating premixed flame. The variations of the consumption speed and the thermal flame thickness with the strain rate in a symmetric counterflow premixed flame are also well predicted. The numerical simulations reproduce the transition from V- to M-shape flame induced by hydrogen addition, and the axial distribution of the heat release agrees with the experimental measurements of OH chemiluminescence. The unit impulse response and the flame transfer function are computed from the LES data using system identification (SysID). The flame transfer functions show a remarkable agreement with the experimental data, demonstrating that the LES-SysID approach using properly calibrated global mechanisms can predict the response of turbulent methane–hydrogen flames to velocity fluctuations. A comparison of the unit impulse response for the various hydrogen additions is presented, and the effect of hydrogen in the flow–flame interaction of the burner evaluated is discussed. [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

29. Resonance-free measuring and excitation of ultrasound

Author

Daschewski, Maxim, Kreutzbruck, Marc, Prager, Jens, Dohse, Elmar, Gaal, Mate, and Harrer, Andrea

Subjects
Computer Science::Sound, Institut für Physik und Astronomie
Abstract

In this contribution we present innovative methods for broadband and resonance-free sensing and emitting of ultrasound. The sensing method uses a polyethylene foil and a laser vibrometer as a broadband and resonance-free sound receiver. In general, this method enables absolute measurement of sound particle velocity and sound pressure in arbitrary, laser beam transparent liquids and gases with known density and sound velocity. The resonance-free emitting method is based on the electro-thermo-acoustic principle and enables, contrary to conventional ultrasound transducers, generation of arbitrary shaped acoustic signals without resonances and post-oscillations.

Published
2015

30. Advanced ultrasonic techniques for nondestructive testing of austenitic and dissimilar welds in nuclear facilities.

Author

Juengert, Anne, Dugan, Sandra, Homann, Tobias, Mitzscherling, Steffen, Prager, Jens, Pudovikov, Sergey, Schwender, Thomas, Chimenti, Dale E., and Bond, Leonard J.

Subjects
AUSTENITIC stainless steel testing, WELDED joint testing, ULTRASONIC testing, NONDESTRUCTIVE testing, NUCLEAR power plant equipment, ACOUSTIC transducers
Abstract

Austenitic stainless steel welds as well as dissimilar metal welds with nickel alloy filler material, used in safety relevant parts of nuclear power plants, still challenge the ultrasonic inspection. The weld material forms large oriented grains that lead, on the one hand, to high sound scattering and, on the other hand, to inhomogeneity and to the acoustic anisotropy of the weld structure. The ultrasonic wave fronts do not propagate linearly, as in ferritic weld joints, but along the curves, which depend on the specific grain structure of the weld. Due to the influence of these phenomena, it is difficult to analyze the inspection results and to classify the ultrasonic indications, which could be both from the weld geometry and from the material defects. A correct flaw sizing is not possible. In an ongoing research project, different techniques to improve the reliability of ultrasonic testing at these kinds of welds are investigated. In a first step (in the previous research project) two ultrasonic inspection techniques were developed and validated on plane test specimens with artificial and realistic flaws. In the ongoing project, these techniques are applied to circumferential pipe welds with longitudinal and transverse flaws. The technique developed at the Federal Institute for Materials Research and Testing (BAM) in Germany uses a combination of ray tracing and synthetic aperture focusing technique (SAFT). To investigate the unknown grain structure, the velocity distribution of weld-transmitting ultrasound waves is measured and used to model the weld by ray tracing. The second technique, developed at the Fraunhofer Institute for Nondestructive Testing (IZFP) in Germany, uses Sampling Phased Array (Full Matrix Capture) combined with the reverse phase matching (RPM) and the gradient elastic constant descent algorithm (GECDM). This inspection method is able to estimate the elastic constants of the columnar grains in the weld and offers an improvement of the reliability of ultrasonic testing through the correction of the sound field distortion. The unknown inhomogeneity and anisotropy are investigated using a reference indication and the special optimization algorithm. Both reconstruction techniques give quantitative inspection results and allow the defect sizing. They have been compared to conventional ultrasonic testing with techniques that are state of the art for components in nuclear power plants. The improvement will be quantified by the comparison of the probability of detection (POD) of each technique. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results